Calendars are used as systems for measuring time into common units. Ancient calendars are based on the movements of the earth and the appearances of the moon and the sun. The present invention is intended for use with the Gregorian calendar which is currently in use throughout Europe and most of the western world. This system approximates the solar year which is the amount of time necessary for the earth to complete one revolution around the sun. A solar year contains 365 days, 5 hours, 48 minutes, and 45.5 seconds. The Gregorian calendar compensates for the partial day by having three 365 day common or non-leap years followed by a 366 day leap year. Additionally, since there remains an 11 minute discrepancy per year, the Gregorian calendar provides that century years which are evenly divisible by 400 are leap years, while other century years are common years (i.e., not a leap year). The use of the leap years in this system complicates calculation of the days corresponding to dates over a wide range of time. The present invention can be used for periods beginning in 1752 since there was a correction eliminating eleven days from Sept. 2, 1752 until Sept. 14, 1752.
Heretofore, perpetual calendars have been known that either utilize at least 12 month tables or which have only a single table of 31 days so that only one day at a time is revealed to the user.